As fad diets come and go, some macronutrients are made into heroes or villains. For a while, fat reduction was popular. Low-carb, low-fat diets were promoted widely. Then, fat was replaced by sugar as "the enemy" and protein became the star. High fat, high protein, and low-sugar ketogenic diets caught on.

All along, one of the key macronutrients played a lesser role: Fiber. Though critically important to our health, fiber hasn't received as much attention as the other nutrients, possibly because it doesn't fit easily into diets heavy on processed foods, it's hard to formulate, and it doesn't usually taste great as a supplement. Existing supplements are typically derived from seed husks and roots, and are typically thick, viscous, and bulky.

Now, it's finally gaining recognition as the forgotten star of a healthy diet. We can eat it in the form of grains, nuts, fruits, vegetables, and legumes. The recommended daily intake is 28 grams a day for women and 35 grams for men, but only 5% of people meet that target and that target was set nearly a century ago and is a mere fraction of what we evolved to need. In fact, since 2005, fiber has been identified as a "nutrient of concern" by the Dietary Guidelines for Americans due to this drastic shortfall in consumption while numbers are worse in Spain and China and declining everywhere.

Eating enough fiber is important because it "is associated with reduced risk of cardiovascular disease, coronary heart disease, stroke, hypertension, certain gastrointestinal disorders, obesity, and metabolic dysfunctions, including prediabetes and type 2 diabetes, and colorectal, gastric, and breast cancers," according to meta-analyses of prospective research studies.

Fiber is also essential for gut health because it feeds the "good" bacteria in your digestive tract. It helps us feel full, regulate our blood sugar, and get a good night's sleep.

Today, some innovative technologies are unlocking ways to add enough fiber back into our diets in a tasty, convenient, and healthy way.

But first, how did this huge consumption gap happen? Let's look back in time.

10,000 years ago, we were a hunter and gatherer species that consumed wild plants, nuts, and animals. Back at this time when our digestive, nervous, and immune system evolved, "billions of microbial organisms have also evolved along with humans to make us their optimal host species," explain the authors of a research article on the gut-brain axis, published in the journal Nutrients. "To achieve this symbiotic relationship, microbes had to evolve functions that were essential for their host's survival, and this involved a direct relationship with the food the host consumed."

Those billions of organisms can break down the fiber humans consume, and extract nutrients that otherwise would be inaccessible to our digestive systems. The seeds, rind, and peels we eat contain long chains of complex sugars chemically bonded together -- which we call fiber -- that our own guts can't process. But some of the organisms in the microbiome can do this job for us -- and can thus extract beneficial biomolecules that support our health.

We ate whole foods, plants, and nuts exclusively for thousands of years, so this symbiosis between our microbiomes and our guts evolved to be mutually beneficial.

"A healthy microbiome -- which is cultivated by a high fiber diet -- is increasingly being linked to positive health status, including the control and prevention of metabolic diseases like diabetes mellitus," says Dr. Amesh Adalja, an infectious disease physician and senior scholar at John Hopkins Center for Health Security.

Then, 200 years ago, everything changed: the Industrial Revolution ushered in semi-processed foods, and eventually ultra-processed foods. Suddenly, we were eating energy-rich foods like cookies, chips, cereals, and pizza that had managed to decouple the sugar we consume from the fiber that had always come along with it and made it safe.

We eat ten times more sugar than we did 200 years ago. And we're eating that sugar without the fibers, protein, and fats that used to go along with it in whole foods. It's not that sugar itself is evil - our cells run on glucose. But we didn't evolve to metabolize purified energy (sugars) isolated from fibers. We used to consume far less, and its effect on our blood glucose used to be tempered by those other macronutrients.

But eating loads of isolated sugars at much higher doses than we evolved to consume can lead to insulin resistance, in which the pancreas becomes unable to convert glucose into energy. Diets high in processed foods can also lead the microbiome to become dysregulated, and induce insulin resistance.

It is no wonder that we see such high rates of obesity and metabolic disorders like diabetes. Of course, some of the most popular medicines today for weight loss are GLP-1s, which you know by name brands like Ozempic and Wegovy. One way to think about those drugs is that they compensate for the fact that, with a severe fiber gap and consequent lack of fiber fermentation, a person doesn't receive the satiety signal.

But if people regularly incorporated adequate fibers back into their diets, it's possible that fewer individuals would need a GLP-1 in the first place. Adding fibers into processed foods we already consume could make them more nutritious and more satisfying. In the future, perhaps GLP-1s could be reserved as medical therapies for extreme cases, rather than commonly used drugs.

Using science, what if we could create non-drug solutions to the fiber gap - and make them cost-effective? Some startups are leading the charge to bring this vision to life.

One.Bio, a startup that recently received an investment from Leaps, has come up with a proprietary process to cut fiber's long chains of tens of thousands of sugar molecules down to merely tens of sugars. This process takes bulky molecules and makes them small enough to dissolve easily into foods and beverages, while retaining the structures necessary to feed the microorganisms in our guts.

The result, CEO Matt Barnard says with a smile, is that the fibers "disappear into the Matrix," meaning that it becomes flavorless and invisible, with the consistency of water with sugar added. It can therefore blend seamlessly into foods and beverages. Rather than having to eliminate fiber to create pleasing products, the One.Bio technology makes it possible to retain high fiber content without sacrificing flavor or texture.

The company's mission is to prevent modern inflammatory diseases and restore a healthy functioning gut by making it easier for people to reach their daily fiber needs. For comparison, you would need to eat a over 6 bowls of Cheerios to get 20 grams of fiber, whereas you could drink a seltzer with One.Bio fiber for the same 20 grams of fiber - without even tasting it.

"We're taking something that is food and keeping it food, rather than letting it be discarded," Barnard says, of the plants that the company transforms into its short chain fibers.

Zya is a startup that takes a different approach to helping solve the fiber gap. Zya has developed an enzyme that, when sprinkled on sugary food, converts up to 30% of that sugar into beneficial dietary fiber after you eat it.

Another buzzy startup is The Supplant Company, which upcycles the waste of agricultural crops like corn husks and oat hulls into a sugar and flour substitute. The company uses enzymes from fungi to convert the plant material into fiber-rich ingredients that retain their taste quality while reducing sugar content.

It's a profound truth that food itself can be medicine. Adding more fiber to our diets is a big step toward better health.